Thermodynamic characterization using high sensitivity differential scanning calorimetry has been carried out in the following areas: Phospholipid Membranes: The effects of isomeric unsaturated long-chain fatty alcohols upon the pretransition of phospholipid liposomes has been interpreted in terms of the effects of these perturbants upon head chain tilt and in terms of the depth of penetration of the alcohol acyl chains in either stabilizing or destabilizing the bilayer. Proteins: The complex, i.e. either asymmetric or polymodal, thermograms obtained in differential scanning calorimetry under conditions of subsaturating ligand concentrations has been accounted for by a model based upon the Law of Mass Action and LeChatelier's principle. Macromolecular Assembly Processes: The complex thermal denaturation profile of the bacteriophage T4 head particle in the small unexpanded form has been identified. The increase in thermal stability arising in the transformation to the expanded lattice form producing large particles has been described.